The present invention is a process for the preparation of primary aminoorganosilanes. The process comprises contacting an cyanoorganosilane with hydrogen gas in the presence of a supported cobalt catalyst. The result of this process is a near quantitative conversion of the cyanoorganosilane to a primary aminoorganosilane.
Primary aminoorganosilanes are useful intermediates for the preparation of aminofunctional silicone fluids, which have wide applications for fabric treatment, personal care products, and as glass coupling agents. A typical process for preparing primary aminoorganosilanes is described in Noll, Chemistry and Technology of Silicones, Academic Press, Inc.. N.Y., 1968, pages 174-176. The process involves the reaction of a haloalkylsilane with an excess of ammonia, as follows: EQU ClCH.sub.2 SiR.sub.3 +NH.sub.3 .fwdarw.H.sub.2 NCH.sub.2 SiR.sub.3 +HCl
This process results in a mixture of primary and secondary amines. Typically the process is run with as much as a 20-fold excess of ammonia, to favor production of the primary amine. This process requires recovering of the ammonia for disposal or recycling and recovery and disposal of the environmental hazardous hydrogen chloride and aminohydrochloride salt by-products.
An alternative route to primary amines, that can avoid these recovery and disposal problems, is formation of cyanoorganosilanes by addition of the Si-H bond to unsaturated nitriles, as follows: EQU R.sub.3 Si--H+CH.sub.2 .dbd.CH--CN.fwdarw.R.sub.3 SiCH.sub.2 --CH.sub.2 --CN
Such procedures are described in Noll, supra, pages 180-181. The nitrile group is subsequently hydrogenated to an amine.
The hydrogenation of nitrile groups is a well known process in organic chemistry. Numerous procedures are described in the patent literature, with considerable attention focused on methods of producing the primary amine without secondary amine formation.
Grunfeld, U. S. Pat. No. 2,449,036, issued Sep. 7, 1948, describes a process run in the presence of nickel or cobalt catalysts, leading to the production almost exclusively of primary amines, where the reduction is carried out in the presence of a strong base soluble in water. Grunfeld states that this process is an improvement over prior art, employing cobalt catalysts, which required the presence of ammonia to drive the reaction toward the production of primary amines.
Martin, U.S. Pat. No. 3.520.932, issued Jul. 21, 1970, describes a process for the preparation of 5-amino-2,2-dialkylpentanols by a one-step catalytic hydrogenation of 4-cyanodialkylbutyraldehydes. The process is run in the presence of a rhodium catalyst and ammonia. Rhodium is reported to be the only catalyst operative in the process.
Butte U.S. Pat. No. 4,186,146, issued Jan. 29, 1980 reports an improved process for the hydrogenation of aromatic nitriles to primary amines. The nitrile is hydrogenated in a solvent system containing added ammonia and a cobalt or nickel catalyst, with the improvement comprising employing an ether as solvent and carrying out the hydrogenation in the presence of water.
Zuckerman, U.S. Pat. No. 4,739,120, issued Apr. 19, 1988, describes an improved process for the catalytic hydrogenation of an organic nitrile group containing compound to a primary aminomethyl group in the presence of a rhodium catalyst, a basic substance, and in a two-phase solvent system comprising an immiscible organic solvent and water.
Lisanke, U.S. Pat. No. 3,046,295, issued Jul. 24, 1962, reports a process for producing primary aminoalkylsilanes. The process comprises contacting, under essentially anhydrous conditions, a cyanoalkylalkoxysilane with a diamino compound, a hydrogenation catalyst, and hydrogen under pressure. The catalyst employed is described as a Raney nickel catalyst.
Therefore, quite unexpectly, it has been found that supported cobalt catalyzes the hydrogenation of cyanoorganosilanes to primary aminoorganosilanes, with near quantative selectivity for the primary aminoorganosilane. This selectivity is achieved without the production of hydrogen chloride and without the addition of ammonia and solvents systems, as previously reported.